What are the symptoms of dehydration?

Dehydration happens when the body loses more fluid than it replaces. You may notice strong thirst, sticky saliva, dry lips, a dry tongue or urine that is darker than usual. Constipation can occur because the bowel has less fluid available to soften stool. Light-headedness may be more noticeable when standing, especially after sweating, vomiting or diarrhoea. Severe fluid loss can lead to confusion, marked weakness or fainting.

Symptoms can overlap with other problems, including a urinary tract infection. Cloudy urine alone does not confirm dehydration, and dark urine can have other causes. Consider the timing of symptoms and any recent illness, heat exposure or reduced drinking.

Take frequent small sips of water. If you have lost fluid through vomiting or diarrhoea, an oral rehydration solution can help replace water and salts; follow the product directions. Rest somewhere cool if heat or exercise contributed. Keep track of whether you are passing urine and whether its colour is becoming lighter. A clinician can advise on fluids if you have kidney, heart or liver disease or have been told to restrict drinking.

Seek urgent medical help for fainting, confusion, inability to keep fluids down, severe weakness, very little or no urine, or difficulty staying awake. Get prompt advice if dizziness persists despite drinking, symptoms follow prolonged heat exposure, or dehydration affects a young child, an older adult or someone with a long-term illness. Contact a clinician if dark urine or excessive thirst continues, because another condition may need assessment.

Ask what may be causing the fluid loss, how much and what type of fluid is suitable for you, and which changes should prompt urgent review. Mention vomiting, diarrhoea, medicines, heat exposure and any change in urination.